1. Technical Field
This invention relates to audio systems and, more particularly, to systems for selectively connecting speech circuits to an audio line in response to voice signals.
2. Description of the Prior Art
Many companies now consider teleconferencing as a cost effective way of communicating among personnel at dispersed locations and thereby reducing the need for business travel. In an audio teleconferencing arrangement, a number of conferees at a location are placed in communication with a number of conferees at one or more remote locations via a telephone connection. The quality of the transmission between the separated groups of conferees is generally dependent upon the position of each conferee with respect to a microphone and loudspeaking device at each location. With a single microphone and loudspeaking device in a room at a conference location, the transmission is subject to degradation because some of the conferees are generally at a greater than optimum distance from the microphone and loudspeaking device.
It is well known to use a plurality of microphones appropriately spaced at each conference location to improve the quality of the conference system. The microphone outputs are summed and the summed output is applied to a communication link then established between locations. In such an arrangement, each conferee can be within an acceptable distance from one of the microphones, whereby speech pickup is of relatively good quality. With all microphones turned on at one time, however, several undesirable effects occur. The total noise pickup is much greater than for a single microphone. The artificial reverberation effects occasioned by the delayed signal pickup from the more remote microphones severely lower the quality of the conference transmission. Further, electroacoustic instability can easily result from the plurality of the always turned-on microphones. It is therefore desirable and also known in the art to provide a switching arrangement which permits only that microphone closest to the talking conferee to be active so that reverberation and noise pickup are minimized.
Such an arrangement is commonly known as a "voting circuit." In the "voting circuit" arrangement, the loudest talker can capture control and lock out the other conferees at his or her location. This automatic switching between microphones, responsive to the highest speech level input alternately appearing at different microphones, however, may also result in transmission interruptions which adversely affect intelligibility and can result in unwanted interference occasioned by transient room noise. For example, a loud noise at one of the conference locations may completely turn off the controlling microphone. Further, since only one microphone is operative at a time, transfer of control from one microphone to another, such as occasioned by the talking conferee moving from one position to another in a room location, can result in speech transmission of varying quality, interruptions in transmission, and reverberation effects which vary with the talking conferee's position.
Various teleconferencing arrangements have been proposed and used heretofore for selecting a single microphone from a plurality of conferee microphones and for transmitting the signal from only the selected microphone. Such arrangements are described in, for example, U.S. Pat. No. 3,730,995 issued to M. V. Matthews on May 1, 1973, U.S. Pat. No. 3,755,625 issued to D. J. Maston on Aug. 28, 1973, U.S. Pat. No. 4,449,238 issued to B. H. Lee, et al. on May 15, 1984, and U.S. Pat. No. 4,658,425 issued to S. D. Julstrom on Apr. 14, 1987.
Another example of a teleconferencing arrangement is disclosed in co-pending U.S. patent application Ser. No. 08/239771 filed on May 9, 1994 on behalf of D. J. Bowen and commonly assigned to the same assignee along with this application. In this co-pending application, a voice-actuated switching arrangement provides for the selection of one or more microphones in accordance with the output signal levels from each of the microphones.
Also, the voice actuated switching arrangement described in the co-pending application employs directional microphones to reduce the degradation of speech signals due to reverberation and noise pickup. These directional microphones are located in a common circular housing and have sensitivity response patterns extending outwardly from the center of the housing. The voice actuated switching arrangement also employs a voting algorithm or process to select for actuation the appropriate number of these microphones for effectively monitoring each person that speaks in a room.
The above-described voice actuated switching arrangement has been satisfactory in minimizing the degradation of the speech signals due to reverberation and noise pickup. It has similarly been satisfactory in causing the microphone selection technique to appear to occur in a quite normal manner without, for example, syllabic clipping as microphones are turned on from the off state. It is nevertheless desirable to simplify the execution of the microphone selection technique so that this technique may be performed in a limited amount of processing time. Such simplification would free a processor more regularly for other necessary computations or enable the use of a less powerful and more economical processor in the switching arrangement.